Three-terminal electronic circuit devices, such as three-terminal regulators and crystal oscillators, are widely used in various electronic circuits. In such a three-terminal electronic circuit device, a functional circuit mounted on an IC chip or the like is sealed by a resin mold or a package made of ceramic or the like and is connected to an external circuit through three leads. The functional circuit sealed by mold material cannot be accessed through any element other than the three leads, thus making it difficult to adjust a characteristic of the functional circuit. Thus, in general, an externally attached circuit for providing a necessary characteristic is employed or another terminal (a terminal that becomes unusable after sealing with the package) for adjustment is used before sealing with the package to write adjustment data.
For example, in a three-terminal 500 mA adjustable positive-voltage regulator 101 described in Non-Patent Document 1, an external circuit as shown in FIG. 3 is used to adjust an output voltage Vo. In the circuit of FIG. 3, the output voltage Vo can be adjusted using a variable resistor R2 and the value of Vo is expressed as Vo=Vref(1+R2/R1)+(IAdj·R2).